The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Combustion timing or phasing is useful to diagnose issues in the combustion process. For a normal combustion process operated under a particular set of parameters, combustion phasing is predictable to within a small range. Combustion cycles deviating from this small range indicate that conditions within the combustion chamber are outside of the expected parameters. Analysis of combustion cycles may be performed in a number of ways.
Known methods to evaluate combustion phasing rely on estimating heat of combustion, the work performed by combustion, or other reactive metrics. These methods review historical data and react to trends or accumulated data points in the combustion data. However, compression-ignition engines and other engine control schemes operate over broad engine conditions. Effective and timely control, including fuel control, fuel tailoring, charge ignition timing control, exhaust gas recirculation (EGR) control, is necessary to meet operator demands for performance and fuel economy and comply with emissions requirements. Furthermore, there is much variability, including that related to: components, e.g., fuel injectors; systems, e.g., fuel line and pressures; operating conditions, e.g., ambient pressures and temperatures; and fuels, e.g., cetane number and alcohol content. The variability in combustion affects heat release and work output from individual cylinders, resulting in non-optimal performance of the engine. A measure of combustion variability based on real-time engine performance would be valuable to diagnose instability in the combustion process and provide information useful to reduce periods of inefficient or high emission operation.
Methods are known for processing complex or noisy signals and reducing them to useful information. One such method includes spectrum analysis through Fast Fourier Transforms (FFT). FFTs reduce a periodic or repeating signal into a sum of harmonic signals useful to transform the signal into the components of its frequency spectrum. Once the components of the signal have been identified, they may be analyzed and information may be taken from the signal.
Change in the engine performance may be apparent in crankshaft speed. A variety of methods are known to measure crankshaft speed. One method utilizes a sensing device in close proximity to a spinning output shaft of the engine. In such known embodiments, the output shaft can be equipped with a target wheel device, indexed in some manner to enable accurate readings of angular velocity of the spinning output shaft. For example, one known embodiment utilizes a metallic wheel with raised indicators in combination with a magnetically sensitive sensor, one index section of the wheel intentionally left without the raised indicators, such that readings from the magnetic sensor clearly measure spinning passage of the raised indicators with a gap in the data stream indicating the passage of the index section. However, many methods are known for measuring the rotational speed of a spinning shaft.
A system capable of transforming signals, such as angular velocity readings from a spinning output shaft, containing information related to combustion into components describing combustion timing in real time would be useful to control sensitive engine control schemes and increase engine efficiency, fuel economy, and emissions control.